1. Field of the Invention
This invention relates to the pipe machining art and more particularly to an improved mandrel arrangement useful in mounting a pipe machining tool for rotation relative to at least one end of a pipe bend to be beveled or otherwise machined. 2. Description of the Prior Art
Many pipe machining tools are designed to be rotated about the center line of a pipe to accomplish a machining operation on the pipe. Two examples thereof are described in U.S. Pat. No. 3,875,832, issued Apr. 8, 1975 entitled Manual Pipe Bevelling Tool and U.S. Pat. No. 3,927,584 issued Dec. 23, 1975 entitled Pipe End Facing and Grooving Machine. U.S. Pat. No. 3,875,832 discloses a manual tool to be rotated about the axis of a pipe adjacent its end for the purpose of cutting a bevel thereon. U.S. Pat. No. 3,927,584 discloses a tool the cutting assembly of which is adapted to rotate about the axis of a pipe to machine a square face and an external annular groove on the end of the pipe for the reception of a pipe coupling element.
In tools of this type, a mandrel is required to mount the tools for rotation. Since the mandrel shaft must be coaxial with the pipe being machined, it is easiest to mount the mandrel arrangement directly to the pipe. Such mandrels must be extremely rigid to provide an accurate cut and to withstand the substantial forces placed thereon, but should also be able to be installed and removed easily relative to a particular length of pipe. The ease of installation and removal is particularly important for use in the field, where pipes are machined with a minimum of sophisticated tools and alignment mechanisms. A mandrel must also be relatively inexpensive to justify extensive field use.
Mandrels exist for use with straight sections of pipe, but I am not aware of any mandrel which is truly satisfactory for use in machining pipe elbows or other bends. U.S. Pat. Nos. 3,875,832 and 3,927,584 illustrate mandrels for use with straight sections of pipe comprising a plurality of longitudinally directed radial fins which may be expanded by tightening an axial draw bar, drawing those fins over a set of radially inclined camming surfaces. The radially outer edges of the fins may thus be caused to engage the inner surface of the pipe in a clamping relationship to rigidly fix the draw bar along the axis thereof. Either the draw bar itself or a hollow bar fitted thereover serves as a mandrel for rotation of the pipe machining tool.
The above-described mandrels are unsatisfactory for use in machining the ends of pipe elbows and other pipe bends because pipe bends generally do not possess the length of straight pipe necessary to engage and retain an expanding fin arrangement. The curved inner surfaces of pipe bends present unique and previously unsolved problems in securing a mandrel. Mandrels for such use must be accurately and rigidly mountable within a pipe bend, and must also be of a simple design allowing quick and easy installation. Further, in many applications, it is desirable to utilize the same basic mandrel arrangement in different schedule pipe elbows. In such applications, of course, the same basic mandrel, with only minor changes or modifications, may be utilized, as desired, to allow proper preparation of the pipe elbow end faces in various sized pipe elbows.